Rotary contact follower for variable inductances



Nov. 19, 1957 M, ALEXY 2,814,023

ROTARY CONTACT FOLLOWER FOR VARIABLE INDUCTANCES Filed July 31, 1953 7,v 1 2 F1 1 w I N IE N TOR.

M22716!!! IRA/ 2x7 d TTORNE 1 United States Patent ROTARY CONTACTFOLLOWER FOR VARIABLE INDUCTANCES Matthew R. Alexy Philadelphia, Pa.,assignor, by mesnc assignments, to the United States of America as represented by the Secretary of the Air Force Application July 31, 1953,Serial No. 371,684 2 Claims. (Cl. 339-9) This invention relates tocontinuously variable inductors and more particularly to rotatableinductors and electrically contact follower means therefor.

The present invention is especially applicable in the field of variableinductances of the type having a continuously rotatable inductanceelement comprising a helical coil having an axis of rotation about whichit turns, an electrically conducting rod mounted substanually parallelto said axis on winch a contact follower tIlCul'lS may move inconnection with the coil. Such contact follower means comprises arotatable metal wheel fixed against rotation with the coil and slidablyheld by said rod in contact with said coil. Means are provided forrotating said coil to vary the contact position of said wheel wnerebythe effective inductance value of said coil is altered through saidcontact means and another point on the coil. The coil mentioned usuallyconsists of a metal wire conductor on a suitable supporting form andarranged as uniformly spaced turns of a helical winding, the rotatablecontact wheel being urged toward and into contact with a single turn ofthe wlnding.

While adapted for relatively slow speed adjustment and lower frequencyranges of operation such as the present radio broadcast band, prior artdevices of this type as represented by the trolley wheel contact meansshown and described in the Patent 2,295,384 of September 8, 1942, toCharles F. Cole, Jr., would be relatively ineffectual at higher speedsand frequency now required. For example, a low contact resistancebetween the wire of the inductor and the shaft on which the contactmeans revolves is very important especially in high frequency circuits.Some devices introduce contact resistance at the point of contact withthe inductor and others internaliy or at the area of contact with theshaft.

Accordingly, it is an object of this invention to provide an improvedrotary contact structure for high speed rel- -atively high frequencytuning inductors and the like which rotary operates with a minimum ofcontact resistance between an inductor and the shaft means on which thecontact structure is mounted.

in many types of communication equipment, such as remotely controlledairplane transmitters and the like, it is often necessary to change thetuning of a resonant circuit very rapidly over a wide frequency range.

Accordingly, it is a further object of this invention to provide animproved rotary contact device for a rotary tuning inductor which iscapable of operation at extremely high speeds of rotation in contactwith said inductor and with a minimum of contact resistance in aconductive connection with said inductor there through.

Very often in inductive windings of the type referred to there may bevariations in certain dimensions of the parts involved, such asvariations in the mean diameter of the successive coil turns, which mayresult in jamming of the contact at high speeds.

Accordingly, it is a further object of this invention to provide animproved rotary follower contact means for a high speed rotary inductorwhich is capable of following any axial or longitudinal eccentricitieswithin the inductor and to maintain a low effective contact-resistanceconnection therewith at all times.

It is also a further object of this invention to provide a rotarycontact system for a variable inductor of the rotary type wherein noperceptible increase in torque is introduced due to dimensionalvariations of the contacting eiectrical elements involved.

In accordance with the present invention, there may be provided a rotaryfollower type contact which is employed as an electrical conductor orvariable tap for a rortary inductor comprising a space wound coil. Thefollower includes four essential elements. The first element is a flatdisk contact having a tapered surface around its periphery provided witha shaft receiving sleeve which extends axially from one side of the diskand an externally threaded radially-split hollow hub extending axiallyfrom the other side. A second flat disk contact element having a taperedsurface around its periphery is provided with a series of slots toreceive the hub of the first flat disk and interlock therewith. A capelement is internally threaded to engage the threaded hub of the firstdisk to contact element. A compression spring is fitted on a sleeve ofthe second disk and inside the hub of the first disk. This spring urgesthe second flat disk into contact with the first flat disk so that thetapered surfaces form a groove at the peripheries of the disks forgripping one turn of the space wound coil and rotating therewith, aswell as traversing the length of the space wound coil when it is rotatedat high speed on a supporting guide shaft extending along the peripheryof the coil.

The advantages of the invention may be seen from the following detaileddescription, when read in conjunction with the accompanying drawing, andthe novel features thereof are defined in the appended claims.

in the drawing:

Figure l is a side elevational view of a continuously variableinductance device provided with rotary contact means embodying theinvention;

Figure 2 is an exploded view in perspective of the rotary contact meansof Pignre l, on a greatly enlarged scale, showing constructional detailsthereof; and

Figure 3 is a detail crossectional view of a portion of the device ofFigure l on the same enlarged scale as Figure 2, showing the operationrelation of the parts of the contact means with an inductor portion ofthe device.

Referring to the drawing, wherein like parts in the various figures aredesignated by like reference numerals, and with reference to Figure 1 inparticular a coil form or drum 23 provides an insulating support for aninductor comprising a uniformly spaced coil winding 30 attached theretoand is mounted to rotate on a shaft 34 journaled in a pair of spaced endplates 24 and 26. The shaft 34 and the inductor on the coil form arerotated through a gear 33 on the shaft 34 and a meshing drive gear 36carried on the end of a drive shaft 40 also journaled in one of the endplates.

A rotary follower or contact device 24} is slidably mounted on a fixedshaft 22 which extends in a direction normal helix angle of coil 3%) andsubstantially parallel to the axis of the coil. Two circular disks 54and 56 are of such a diameter as to make contact with a single turn ofthe coil 30, substantially as shown in Figure 3.

Upon rotation of the coil form 28, the rotary contact device 29 is movedlongitudinally in a direction substan tially parallel to the axis of thecoil 3t}. Different rotary follower positions are illustrated by thedotted lines in Figure 1. Movement of the rotary follower effects achange in the inductance of the coil 30 with respect to the point ofcontact. For tuning resonant signal circuits the inductor is connectedat one end such at a terminal to ground through the shaft 34 while theshaft 22 follower 24), as will be-desc rihed, permits extre'mely'goodelectrical 'contactbetween the coil 36 and the rotary fol lower 2!} whenthe speed of rotation of the coil is extremely high. Such highspeedresponse is oftenn'ecessary in communication equipment associatedwith aircraft andthe like. 7

Referring more particularly to Figure 2 of the drawing, the rotaryfollower contact 20 is shownin an exploded view. A first flat disk 56has an integral sleeve 56a on one side which is adapted-to receive thefixed shaft 22 with a smooth rotational fit. On theother side of thisdisk is an externally threaded radially-split hollow huh 56b. A secondflat disk 54*has an'integral sleeve 54:: on one side which isalso'adapted to'receive th'e fixed shaft 22 with a smooth rotationalfit. Openings or slots 54]) in the second disk are adapted to receivethe hollow hub 56b of the first disk when the two disks are moved intoface-toface contact with each other as indicated in Figure 3. Both disks54'and 56 have an angularly tapered surface 58 around their peripheraled es. A cap element t) is internally threaded (the threads not shown)and adapted to engage the externally threaded hub 56b of the first flatdisk. A compression spring 52 is adapted to be positioned on the sleeve54a of the second flat disk 54. Thisspring is'disposed between thesleeve 54a and the hub 56b so that it biases the second disk 54 intocontact with the first disk 56 when the cap 50 is threaded on to the hub56b. The angular tapered surfaces 58 provide a groove to permit betterelectrical contact between the two disks and the coil by providing agreater surface area on the disks to contact the coil.

Referring more particularly to Figure 3, the rotary follower contact 29is mounted on the fixed shaft 22 with the fiat disks 54 and 56inoperating engagement with the coil 3%). The spacing between the shaft22 and the spaced coil 36 is such that there is a pressure between therotary follower 2d and the engaged turn of the coil. This pressure is toinsure good electrical contact between the coil and the follower. Thespacing between the shaft 22 and the spaced coil 34} is such that thepositioning of these elements will result in a small gap between thedisks 56 and 54 with the turn of the inductor forced between them asshown. In the event that there are any variations in the dimensions ofthe coil 30 the pressure exerted by the coil winding will cause the gapbetween the two disks 54 and 56 to vary against the biasing action ofthe spring 52; Despite any variations in dimensions of the coil, it isseen that the rotary follow still maintains firm electrical contact withthe coil.

The present invention provides a means whereby the lowest possiblecontact resistance between the wire of the inductor and the shaft itrotates about, by reducing to the minimum the number of elementsinvolved. It may be seen that the fiat disk 56 electrically connects thetap on the coil 30 to the fixed shaft 22. In parallel therewith the disk54 electrically connects the tap on the coil directly with the shaft 22.This feature is of particular importance for high speed operation athigh frequencies.

This invention further provides simplified mechanical structuresincludingmeans to compensate for variations 7 from the nominaldimensions of the parts involved. This feature is very important forhigh speed operation. In the construction of the present embodiment ofthe invention, the coil conductor is resiliently gripped between tworelatively movable dish edges each of which may move independently ofthe other to conform to irregulations in the conductor pulse. Thisfeature has contributed to the successful operation of the device inhigh speed remote control tuners for mobile communication systems andthe like which operate at relatively high frequencies.

Another feature provided in accordance with this inusual rollers forcontact members.

I V p 4 i vention is that involving the means for providingminimumtorqu'e with no perceptible increase even with dimensionalvariations of the elements involved. Mounting of the follower at anangle normal to the helical angle of the coil permits the minimum torqueeven when the coil is rotated at high speeds.

The compact and sturdy construction of the rotary follower describedin-this'z application is such that op-' eration at very high speed's'up-to-l800 or more revolutions per minute is possible.

The rotary follower jsuch as described is subject to less friction andresulting};wear-than wiper arms or the Consequently there is the furtheradvantage" of longer wear" to be "derived from the use of the rotaryfollower, such as described, as a contact member in a high frequencyvariable in ductor unit.

What is claimed isz 1. A rotary. follower contact device for spacewoundrotary variable coils and' the like comprising a first flat disk contactelementhavingan axially extending sleeve adapted. to receiveaguideshaftonone side and having an externally threaded radially; splithollow hub axial-.

ly extendin'gtherefromand a tapered surface about the periphery.thereof-on the other side, a second fiat disk contactelementhavin'geonone 'side' an axially extending sleeve; adaptedtoreceive said guide shaft and having slots extending throughsaid'element toreceive and in-- terlock' with said'hub andhaving atapered surface around the periphery of-tne other side of said secondelement, said tapered surfaceson said contact elements being on facingsides of said elements'to-form a groove around the periphery of saiddevice, a cap element internally threaded and attached to the threadedhub of said first fiat diskcoutactelement; and a'compression springsurrounding the sleeve of said second disk and locatedin the-hub of saidfirst disk, whereby the. spring is efiective to bias the second diskinto contact with the first disk.

2. Arotary follower contact device for a space wound inductance coil'andthe like comprising in combination a first circular flat disk, .atapered surface portion about the periphery of said first disk on oneside, an integral axially extending sleeve member on the other side ofsaid first disk adapted to receive and rotate on a guide shaft, aplurality ofthreaded radially split hub elements extendingraxially, fromthe one side of said first disk, a second circular flat disk havingcentral openings adapted to receive said threaded hub elements of saidfirst disk, a second sleeve member extending axially from one sideofsaid second circular'flat-disk adapted to receive and rotate on saidguide-shaft, a tapered surface portion about the periphery of saidsecond disk on the other side, said disk being mounted with said taperedsurface portions adjacent to form a peripheral groove extendingaroundthe periphery ofsaid device, a spring member disposed around saidsecond sleeve member of said second disk, and an internallythreaded capmember detachably secured to the threaded portions of said threaded hubelements of said first disk to compress the spring member andeifectre'silient biasing of said second disk towards said-first disk.

References'Cited'in the file of this patent

